The advent of neuroimaging has brought medical attention to the frequency of unsuspected white matter lesions in the brains of elderly people. In 1987 Hachinski suggested the term "leuko-araiosis" to identify such white matter abnormalities detected by computed tomography and magnetic resonance imaging to emphasize that their etiology and clinical relevance require clarification. Since then, leuko-araiosis has been recognized among approximately ten percent of apparently normal, elderly people over age sixty-five. The severity and frequency of leuko-araiosis increases with advancing age, risk factors for stroke, history of strokes particularly of the lacunar type and dementia of both the vascular and Alzheimer type. Current concepts concerning the pathogenesis and neurological concomitants of leuko-araiosis are reviewed. The etiology of leuko-araiosis may be heterogeneous but is most likely ischemic in nature. However, as white matter lesions progress among the elderly they are likely to become associated with cognitive impairments and motor dyspraxias presumably resulting from cortico-subcortical disconnections, particularly involving the frontal cortex and basal ganglia and may themselves be considered a radiological "risk factor" or precursor for dementia.